The present invention relates to a calcined member for arc-extinguishing chambers that are employed for electromagnetic contactors for high-voltage applications and for electromagnetic circuit breakers.
In the conventional arc-extinguishing chambers employed for high-voltage electromagnetic contactors and electromagnetic circuit breakers which break heavy currents of high voltages, it is accepted practice to provide the arcing path with separator walls maintaining a suitable distance, i.e., to form an arcing labyrinth in order to lengthen the arc that takes place between the contacts. Grids are often used to form the arcing labyrinth as shown in FIGS. 1, 2 and 3. In the drawings, reference numeral 1 denotes a plurality of grids each having a nearly V-shaped groove 2 that runs from the lower end toward the higher direction and that is deviated toward one direction as illustrated in detail in FIG. 3(a). The grids are arrayed maintaining a predetermined distance as shown in FIG. 1, in such a manner that the V-shaped grooves 2 are disposed in a zig-zag manner to form an arcing labyrinth as shown in FIG. 3(b). The grid 1 is usually made of a porcelain-type material which is obtained by molding a powder of zircon porcelain, zircon-cordierite porcelain or alumina porcelain, followed by calcining in a kiln heated at 1100.degree. to 1400.degree. C. for about 24 hours. Reference numerals 4, 4' denote arc horns, and 5, 5' denote splitters to which the arc horns 4, 4' are fastened by screws. Like the grids 1, the splitters are made of a porcelain such as zircon porcelain or zircon-cordierite porcelain which has increased resistance against the heat and arc. The splitters 5, 5' also serve as side plates. Reference numerals 6, 6' denote stepped portions formed in the splitters 5, 5' so as to form a ceiling for the ends of the arc horns 4, 4'. Reference numeral 7 denotes a deflector plate, 8 and 8' denote shields, and 9 and 9' denote a pair of side plates.
In the thus constructed arc-extinguishing chamber, the arc which develops across the contactors (not shown) travels to a position of between the arc horn 4 and the arc horn 4'. Here due to the function of magnetic flux and current generated by a blow-out coil, the arc travels upwards from the position A-A' to the position B-B' in FIG. 1. Therefore, the arc is lengthened and is quenched through the arcing labyrinth formed by the grids 1. As the arc reaches the ends of the arc horns 4, 4', feet of the arc come into contact with the stepped portions 6, 6' and are temporarily interrupted from moving upwards. In this case, the central portion of the arc belches out of the arc-extinguishing chamber being divided into two by the deflector plate 7. Therefore, the arc is further lengthened as indicated by C-C' in FIG. 1. Since the feet of arc have been stopped at the ends of the arc horns 4, 4', however, the arc is sufficiently quenched by the splitters 5, 5' which have increased resistance against the heat and is extinguished before it comes out of the arc-extinguishing chamber. The arc is thus extinguished.
Grids 1 which form the arcing labyrinth are usually constructed in the below-mentioned two manners.
One method consists of using grids 1 of flat plates of FIG. 3(a) as mentioned already, arraying them alternatingly as shown in FIG. 3(b), and stuffing an inorganic material such as asbestos-type material 10 among the grids 1 to eliminate clearance. According to this method, however, tremendous amount of labor, extended periods of time and increased manufacturing costs are required, inviting a defect of decreased insulation as a result of sucking the moisture. Further, the grids 1 must be calcined in a kiln heated at 1100.degree. to 1400.degree. C. for 24 hours. Therefore, distortion or warping tends to develop on a plane of the grids. Further, the grids have small resistance against impact, and are often broken during the assembling operation, or during the transportation and checking.
Another method consists of using grids 1 which have side plates 3, 3' on both sides as shown in FIG. 4(a), and combining them as shown in FIG. 4(b). Even in this case, the arc belches through the side plates 3. 3' of grids 1 in the X and Y directions. Therefore, belching of arc must be prevented by using an expensive inorganic material such as mica or zircon porcelain (asbestos is not used since it has poor hygroscopic property). Further, the grids 1 are often warped, or broken during the operations of assembling, transportation and checking, since they are made of a zircon porcelain, zircon-cordierite porcelain or alumina porcelain, through the step of calcining at 1100.degree. to 1400.degree. C. for more than 24 hours.
As mentioned above, the procelain-type material produces very little gas when it is used as an arc-resistant material and, hence, does not exhibit the function to extinguish the arc by the gas. The porcelain-type material, however, exhibits excellent resistance against high temperatures, exhibits very high insulation resistance on the arcing surface under high-temperature conditions, and exhibits increased arc-resistant property. Therefore, the porcelain-type materials have heretofore been extensively used for grids for arc-extinguishing chambers and for arc-extinguishing side plates. The porcelain-type materials, however, have poor moldability and poor dimensional precision, and are subject to be damaged upon receipt of mechanical impact and vibration.